The following relates to the welding arts, nuclear reactor arts, nuclear fuel rod arts, nuclear power generation arts, and related arts.
In a typical nuclear reactor, the reactor core generally includes a number of fuel assemblies each of which is made up of an array of fuel rods. Each fuel rod includes a tubular cladding containing fuel pellets comprising fissile material. The cladding is sealed by upper and lower end caps or plugs. The nuclear reactor core is made up of an array of such fuel rods, and is disposed in a pressure vessel containing primary coolant (typically water, although heavy water or another coolant is also contemplated). The primary coolant flows through the nuclear reactor core and is heated by the radioactive core. In a typical boiling water reactor (BWR) configuration, the heated coolant boils to form primary coolant steam that is piped out of the pressure vessel and used to drive a turbine. In a typical pressurized water reactor (PWR) configuration, the primary coolant remains in a subcooled state and is piped through steam generators located outside of the vessel to heat secondary coolant that drives a turbine. In a variant integral PWR configuration, the steam generators are located inside the pressure vessel and the secondary coolant is pumped into the steam generators.
In general, each fuel rod includes a column of nuclear fuel pellets loaded into a cladding tube, and end plugs secured to opposite (e.g., bottom and top) ends of the tube. The end plugs should provide a reliable seal to prevent leakage of primary coolant into the fuel rods. In known approaches, the top and bottom end plugs are girth or butt welded to the opposite ends of the tube, for example by fusion welding or solid state welding.
Resistance welding of the end plugs to the cladding is also known wherein a cladding tube is butted against an end plug. In this approach, a high current is passed between the cladding and the end plug which is compressively loaded. Resistance at the interface between the end plug and the cladding generates localized heating resulting in a diffusion bond. While resistance welding has many desirable attributes, the process has some shortcomings. For example, non-destructive weld examination is generally not feasible. Bond quality can also be susceptible to some contaminates, in some cases, with no means of detection. Weld upset, or flash, typically must be mechanically removed or suppressed in a post-weld process that complicates the processing.